Person: Taylor, Jacob
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Taylor, Jacob
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Publication Dynamic Nuclear Polarization in Double Quantum Dots(American Physical Society, 2010) Gullans, Michael John; Krich, Jacob Jonathan; Taylor, Jacob; Bluhm, Hendrik; Halperin, Bertrand; Marcus, C; Stopa, Michael P; Yacoby, Amir; Lukin, MikhailWe theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the buildup of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called ‘‘dark states’’, and the elimination of the difference field. We show that in the case of unequal dots, buildup of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, buildup of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process.Publication Qubit Protection in Nuclear-Spin Quantum Dot Memories(American Physical Society, 2009) Kurucz, Z; Sørensen, M W; Taylor, Jacob; Lukin, Mikhail; Fleischhauer, MWe present a mechanism to protect quantum information stored in an ensemble of nuclear spins in a semiconductor quantum dot. When the dot is charged the nuclei interact with the spin of the excess electron through the hyperfine coupling. If this coupling is made off-resonant it leads to an energy gap between the collective storage states and all other states. We show that the energy gap protects the quantum memory from local spin-flip and spin-dephasing noise. Effects of non-perfect initial spin polarization and inhomogeneous hyperfine coupling are discussed.Publication Robust Optical Delay Lines with Topological Protection(Nature Publishing Group, 2011) Hafezi, Mohammad; Demler, Eugene; Lukin, Mikhail; Taylor, JacobPhenomena associated with the topological properties of physical systems can be naturally robust against perturbations. This robustness is exemplified by quantized conductance and edge state transport in the quantum Hall and quantum spin Hall effects. Here we show how exploiting topological properties of optical systems can be used to improve photonic devices. We demonstrate how quantum spin Hall Hamiltonians can be created with linear optical elements using a network of coupled resonator optical waveguides (CROW) in two dimensions. We find that key features of quantum Hall systems, including the characteristic Hofstadter butterfly and robust edge state transport, can be obtained in such systems. As a specific application, we show that topological protection can be used to improve the performance of optical delay lines and to overcome some limitations related to disorder in photonic technologies.Publication Coherence of an Optically Illuminated Single Nuclear Spin Qubit(American Physical Society, 2008) Jiang, Liang; Dutt, M; Togan, E; Childress, Lily; Cappellaro, Paola; Taylor, Jacob; Lukin, MikhailWe investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal electronic spin associated with a nitrogen-vacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.Publication Quantum Repeater with Encoding(American Physical Society, 2009) Jiang, Liang; Taylor, Jacob; Nemoto, Kae; Munro, W J; Van Meter, Rodney; Lukin, MikhailWe propose an approach to implement quantum repeaters for long-distance quantum communication. Our protocol generates a backbone of encoded Bell pairs and uses the procedure of classical error correction during simultaneous entanglement connection. We illustrate that the repeater protocol with simple Calderbank-Shor-Steane encoding can significantly extend the communication distance, while still maintaining a fast key generation rate.Publication Exchange Control of Nuclear Spin Diffusion in a Double Quantum Dot(American Physical Society, 2010) Reilly, David J.; Taylor, Jacob; Petta, Jason R.; Marcus, C; Hanson, Micah P.; Gossard, Arthur C.The influence of gate-controlled two-electron exchange on the relaxation of nuclear polarization in small ensembles \((N \sim 10^6)\) of nuclear spins is examined in a GaAs double quantum dot system. Waiting in the (2,0) charge configuration, which has large exchange splitting, reduces the nuclear diffusion rate compared to that of the (1,1) configuration. Matching exchange to Zeeman splitting significantly increases the nuclear diffusion rate.Publication Coherent Spin Manipulation in an Exchange-Only Qubit(American Physical Society, 2010) Laird, Edward A.; Taylor, Jacob; Di Vincenzo, David P.; Marcus, C; Hanson, Micah P.; Gossard, Arthur C.Initialization, two-spin coherent manipulation, and readout of a three-spin qubit are demonstrated using a few-electron triple quantum dot. The three-spin qubit is designed to allow all operations for full qubit control to be tuned via nearest-neighbor exchange interaction. Fast readout of charge states takes advantage of multiplexed reflectometry. Decoherence measured in a two-spin subspace is found to be consistent with predictions based on gate voltage noise with a uniform power spectrum. The theory of the exchange-only qubit is developed and it is shown that initialization of only two spins suffices for operation. Requirements for full multiqubit control using only exchange and electrostatic interactions are outlined.